Solid rivets are probably the oldest and most widely used fasteners in the industry. They are inexpensive to manufacture, do not require close tolerance holes, and they are easily installed. Riveted structures usually have an extended service (fatigue) life because of the hole-filling characteristics of the rivet. When rivets are driven, the rivet shank expands and tends to fill the hole. This eliminates relative movement between the joined structural members, thus, providing an extended fatigue life.
Blind rivets are designed to be installed from one side of the structure being joined. Thus, they are used where access from the opposite side, for positioning the bucking bar, is difficult or impossible to accomplish. While the blind rivet may be more expensive to manufacture, they can be rapidly installed by only one person using relatively inexpensive hand held machines. A typical blind fastener made to NAS1398 or 1399 standards is the Cherry Lock.RTM. manufactured by Cherry Aerospace Fasteners, a Division of Textron Incorporated. Rivets of this type consist of a hollow sleeve, a spindle moveably mounted therein, and a locking collar. The spindle consists of a stem for gripping by the installation tool in frangible attachment to a shear pin portion. A mandrel for upsetting the end of the sleeve for locking the rivet in place is attached to the opposite end of the shear pin portion. The sleeve incorporates a head, which may be a portruding or flush-head type, and the opposite end protrudes from the other side of the structures being pinned. The locking collar is moveably mounted on the stem. The rivet is installed by placing the above-described assembly in a hole in the structures to be joined. The tool is used to hold the sleeve in the hole and simultaneously pull the stem upward. This causes the shear pin portion to slide up through the sleeve and, thereafter, the mandrel portion to deform the end of the sleeve extending out the other side of the structure. This will lock the sleeve in place. Simultaneously, a groove on the shear pin portion becomes aligned with a groove or slot in the head of the sleeve and the locking collar is wedged therein by the tool locking the shear pin portion in place. Thereafter, continued pulling on the stem causes it to separate from the shear pin portion. Examples of this design and others can be found in the following patents: U.S. Pat. No. 4,407,619, Blind Fastener with Deformable Clamping Means, G. Siebol; U.S. Pat. No. 4,364,697, Blind Fastener Assembly, L. S. Binns; U.S. Pat. No. 4,230,017, Pull-Type Blind Fastener Construction, D. J. Angelosanto; U.S. Pat. No. 4,219,924, Process for Installing Lock Spindle Blind Rivet, R. R. Luhm; U.S. Pat. No. 4,143,580, Lock Spindle Blind Rivet, R. R. Luhm; U.S. Pat. No. 4,451,189, Bulb Rivet, J. D. Pratt; U.S. Pat. No. 4,432,679, Lock Spindle Blind Fastener for Single Action Application, D. J. Angelosanto, et al.; U.S. Pat. No. 4,246,828, Blind Fastener, E. K. Tamashiro; U.S. Pat. No. 4,177,710, Blind Fastener, J. Matuschek; U.S. Pat. No. 4,127,345, Lock Spindle Blind Fastener for Single Action Application D. J. Angelosanto, et al. However, such blind fasteners are not noted for their fatigue life.
Pins installed with an interference fit, which put residual hoop tension stresses around the hole, are used to enhance the fatigue life of structures. These pins are expensive and require very close tolerance holes (after requiring reaming) and, therefore, are expensive to install One such fastener is the Hi-Tigue pin, manufactured by the Hi-Shear Corporation, Torrance, Calif. This pin used a small integral spherical shaped ring near the threaded end to cold work the hole.
It would be more desirable to place residual hoop compression stresses around the hole. One technique to accomplish this, which has been developed by the Fatigue Technology Corporation, Seattle, Wash., is to expand the hole with a removable sleeve and mandrel. The mandrel, while it is being pulled through the hole, stresses the material around the hole beyond the proportional limit in hoop tension. Thus, when the mandrel is removed, the material around the hole recovers elastically and forms residual hoop compression locally around the hole.
Applicants have developed solid protruding-head and flush-head rivet designs which are, disclosed in co-pending patent applications: Ser. No. 657,300 Controlled Expansion Flush-Head Rivet Design and Method of Installing Same, Ser. No. 657,700 Controlled Expansion Protruding-Head Rivet and Method for Installing Same, Ser. No. 803,749 Shaped Tail for Hold Expanding Rivet, and Ser. No. 676,464 Controlled Expansion Flush-Head Rivet Design and Method of Installing Same. This controlled expansion concept is not believed to have been previously applied to a blind rivet.
Further, in none of the above discussed blind rivets has an attempt been made to make all critical dimensions of the sleeve, spindle, and locking collar a function of the sleeve outer diameter. While in most cases standard rivet sizes will suffice, there are instances where special diameters (switching from inch to metric sizes, etc.) are required. Thus, a rivet having all the critical dimensions based on the shank diameter would be advantageous, since design and test time required to insure necessary static tension, shear strength, and fatigue life would be reduced to a minimum.
It must be noted however that, solid rivet designs have been previously proposed. For example, in the winter 1962/63 in Advanced Fastener Applications Engineering there is an article titled, "The Real Strength of Rivets" wherein a protruding-head rivet design is proposed having several of the dimensions thereof based on ratios of the shank diameter. These ratios are not keyed to the minimum and maximum shank diameters. Applicants, in their previously mentioned co-pending patent applications Ser. Nos. 657,300, 657,700, and 676,464 solid rivet designs, in addition to having the controlled expansion, have all their critical dimensions based on ratios of the minimum and maximum allowable shank diameter i.e., the dimension ranges are between an X value times the minimum shank diameter of the rivet and a Y value times the maximum shank diameter. Thus, the tolerance of all the critical dimensions of the rivets are defined. The ratios X and Y are selected to provide the contolled expansion.
Therefore, it is a primary object to provide a blind fastener that, when driven, obtains controlled expansion of the hole, placing residual hoop compression stresses in the hole wall and thereby increasing the fatigue life.
It is another primary object of the subject invention to provide a blind fastener wherein all critical dimensions thereof are ratios of the sleeve shank outer diameter.
A further object of the subject invention is to provide a blind fastener wherein controlled expansion of the hole is accomplished by use of a cold working mandrel frangibly attached to the shear pin portion of the spindle.
A still further object of the subject invention is to produce a blind fastener that can be installed and driven in holes produced with standard twist drills.
An additional object of the subject invention is to provide a blind rivet that can be installed with standard tools.